During hard exercise, glucose derived from glycogen in muscles is utilized, and anaerobic glycolytic reaction proceeds and ATP necessary for contraction of muscles is synthesized. Then, lactic acid as a metabolite is stored and intramuscular pH tends to decrease, whereby the efficiency of muscle contraction is reduced. This condition is called metabolic acidosis, and it is believed that this condition results in muscular fatigue. Accordingly, in order to control the muscular fatigue by continuous exercise, it is important not to cause metabolic acidosis.
In recent years, it is popular among athletes to intake creatine as a supplement. It is known that creatine is converted to creatine phosphate in the body and has a function of transferring energy as a high energy phosphate compound, and that creatine is a component essential for synthesis of ATP, and that by the intake of creatine, the creatine amount in muscles is increased and the performance of extreme sports or exercise will be improved (Harris, R. C. et al: Clin. Sci., 83, 367-374, 1992).
Further, if glycogen as an energy source becomes insufficient, body fat tends to be easily utilized and at the same time, amino acid in blood is converted to energy. Accordingly, it has also been attempted to increase the amino acid concentration in blood as high as possible, to utilize it as an energy source and improve the muscular fatigue and the decline of muscular strength. Particularly utilizable amino acid as the energy source is a branched amino acid (e.g. leucine, isoleucine and valine). For example, JP-A-58-165774, JP-A-7-25838 and JP-A-2000-26290 disclose the use of the above branched amino acid as foods.
Further, JP-A-8-198748 and JP-A-9-249556 disclose that for the purpose of improving athletic functions and providing effects for recovering from fatigue, the fluctuation of amino acid in blood is controlled by administering an amino acid composition constituted in accordance with the amino acids contained in saliva secreted by larvae of a verpine wasp (Vespar genus).
Incidentally, an extract obtainable from fishes, shellfishes, fowl, flesh or the like, contain various amino acids, and generally widely utilized as a seasoning. However, physiologically active functions thereof have hardly been researched.